The present invention relates to a radio transmitter and a radio transmission method capable of compensating the spread of a band width of a power spectrum while a transmission wave is transmitted in burst transmission.
FIG. 1 is a diagram showing a configuration of a conventional radio transmitter. In FIG. 1, the reference number 1 designates an amplifier for amplifying a RF signal that has been modulated based on GMSK (Gaussian filtered Minimum Shift Keying) modulation, and 2 denotes a coupler for outputting a large part of the power of the RF signal that has been amplified by the power amplifier 1 and for outputting the remaining part of the power of the RF signal to a detector indicated by the reference number 3. This detector 3 detects a power value of the RF signal transferred from the coupler 2. The reference number 4 designates a controller for generating a reference power value corresponding to the transmission power of the RF signal in burst transmission. This controller 4 comprises a CPU, a DSP, a power source circuit, an audio circuit, a digital to analogue converter, and other components. The reference number 5 denotes a differential amplifier for comparing the power value outputted from the detector 3 with the reference power value outputted from the controller 4 and for generating a feedback signal in order to control the gain of the power amplifier 1.
Next, a description will be given of the operation.
In general, each of mobile communication devices represented by cellular telephones incorporates an APC (Automatic Power Control) circuit in order to control the range of a transmission power of the RF signal as a transmission wave within a specified range to be used in a radio communication system even if the change of circumstance conditions such as a voltage of a power source or an ambient temperature happens.
In the configuration shown in FIG. 1, because a feedback signal is fed to the power amplifier 1, the gain of the power amplifier 1 is so controlled that the transmission power is set into a constant range. That is to say, because the APC circuit is a negative feedback circuit, in order to output the RF signal having a constant power value, the gain of the power amplifier 1 is decreased when the power of the RF signal is increased, and conversely, the gain of the power amplifier 1 is increased when the power of the RF signal is decreased.
When TDMA (Time Division Multiple Access) is used as a communication access, the RF signal as the transmission wave is transmitted in burst transmission, not transmitted continuously.
FIG. 2 is a diagram showing an example of a configuration of a TDMA frame for GSM (Global System for Mobile Communications) that has been used in Europe and all over the world. The time interval of one TDMA frame is 4.62 ms. The TDMA frame has the following configuration.
One TDMA frame: eight time slots:4.62 ms. When the RF signal is transmitted in burst transmission by using the slot (2) in the current TDMA frame shown in FIG. 2, the following RF signal is transmitted by using the time slot (2) in the following TDMA frame.
FIG. 3 is a diagram showing a transmission state of the TDMA frame in the radio transmitter. In FIG. 3, the radio wave is transmitted during the transmission ON state and not transmitted during the transmission OFF state in burst transmission.
However, the effect of the rising edge and the falling edge of the transmission wave on a frequency axis to the power spectrum is not ignored. In general, the time interval of each of the rising edge and the falling edge of the transmission wave is determined based on a system standard to be applied. For example, FIG. 4 shows a time interval of each of the rising edge and the falling edge of the transmission wave in GSM standard. The time interval in the part other than the rising edge and the falling edge of the transmission wave is changed according to the kind of transmission burst. On the other hand, the time interval of each of the rising edge and the falling edge must be set within the time interval of 28 us.
In a case that the RF signal transferred from an actual radio transmitter is applied to the transmission time mask shown in FIG. 4, the rising edge and the falling edge of the RF signal adequately satisfy the GSM standard when a time slot as one transmission interval of the RF signal has a completely square wave. However, because the RF signal is a pulse sequence of the square wave and the power spectrum of this RF signal requires an infinite band, a side-band of the RF signal is increased and the RF signal does not satisfy the transmission spectrum standard.
In order to avoid this drawback, in general, a band limitation is used. This method uses a band limitation filter such as a cosine roll-off filter, through which a base-band signal to be modulated is transferred, that satisfies a Nyquist standard (intersymbol interference of zero). However, this method requires that a system to be used after the modulation based on the base-band signal must be a linear basically. For this reason, this method is commonly used in systems using a linear modulation method such as xcfx80/4 shift QPSK modulation. On the contrary, the GMSK modulation used in this conventional example shown in FIG. 1 has a constant envelope curve, and in terms of a current consumption, that is to say, of a talk time of a mobile device, most power amplifiers of the linear type are not used as the power amplifier 1 shown in FIG. 1.
In the band limitation in the power spectrum in the conventional example shown in FIG. 1, the rising edge and the falling edge of the RF signal as an actual transmission wave are controlled by adjusting the gain of the power amplifier 1 based on the feedback signal. Substantially, the gain of the power amplifier 1 is controlled based on a reference power value outputted from the controller 4 and data (as these reference power values) corresponding to the rising edge and the falling edge of the transmission wave are stored in a memory in the controller 4. In the adjusting stage for the radio transmitter, it may be acceptable that adjusting values as the data are stored in the memory while observing the time mask on the time axis of the power of the RF signal and the power spectrum on the frequency axis, or calculated adjusting data are prepared in advance and then stored in the memory.
For the calculation of the data, there are methods to calculate the data based on the theory of window functions such as a Hamming window or a Hanning window, for example. FIG. 5 shows three cases of the band limitation to the RF signal by the power amplifier 1. In FIG. 5, when the RF signal is inputted shown in FIG. 5(a), and the gain of the power amplifier 1 is controlled based on the feedback signal as shown in FIG. 5(b), the output of the RF signal becomes the waveform shown by the solid line in FIG. 5(c). This waveform means the window that has been cut shown in FIG. 5(b) when the RF signal is considered as a square pulse (a pulse sequence). When this window is considered as a time function, the data described above can be calculated. In all of the cases, the time interval of each of the rising time and the falling time of the RF signal satisfies the standard defined by the system using this RF signal.
Because the conventional radio transmitter has the configuration described above, the controller 4 can control preciously the spread of the band of the power spectrum only when the shape of the reference power value on the time axis outputted from the controller 4 is equal to the shape of the RF signal on the time axis. However, in an actual case, because the shape of the reference power value on the time axis is not always equal to the shape of the RF signal on the time axis, it must be necessary to adjust the reference power value of each radio transmitter while radio transmitters are manufactured. In addition, even if the shape of the reference power value on the time axis is equal to the shape of the RF signal on the time axis, the total gain of the transmitter system also varies widely if there is the variations of characteristics of the power amplifier 1, the coupler 2, and other circuit components incorporated in the radio transmitter. The shape of each of the rising edge and the falling edge of the RF signal is thereby distorted. When the degree of the distortion is greater, it is necessary to adjust the reference power value.
Accordingly, an object of the present invention is, with due consideration to the drawbacks of the conventional technique, to provide a radio transmitter and a radio transmission method capable of suppressing the spread of the band of the power spectrum preciously without adjusting the reference power value after manufacturing.
In carrying out the invention and according to one aspect thereof, there is provided a radio transmitter capable of calculating an ideal value by adding an error component at a reference time to a theoretical value, and for comparing the ideal value with the error component in order to generate a reference level. Thereby, the present invention has the effect that it is possible to preciously suppress the spread of the band of the power spectrum without adjusting the reference power value after manufacturing.
According to another aspect of the present invention, there is provided a radio transmitter capable of controlling a gain of a first amplifier means based on the error component detected by a detection means. Thereby, the present invention has the effect that it is possible to preciously suppress the spread of the band of the power spectrum without adjusting the reference power value after manufacturing.
According to another aspect of the present invention, there is provided a radio transmitter incorporating a calculation means for calculating a theoretical value showing a burst waveform by using a window function. Thereby, the present invention has the effect that it is possible to easily get the theoretical value showing the burst waveform.
According to another aspect of the present invention, there is provided a radio transmitter incorporating a calculation means for calculating an envelope curve value based on the base-band signal, for calculating an error component by comparing the envelope curve value at the reference time with the specified power value, and for calculating the theoretical value by adding the error component to the envelope curve value per time. Thereby, the present invention has the effect that it is not necessary to calculate the theoretical value by using the window function and it is possible to apply the present invention to the compensation of the distortion in a transmitter chain in a device corresponding to a system based on the linear modulation method.
According to another aspect of the present invention, there is provided a radio transmitter incorporating a detection means and a generation means, the detection means comprises a first subtracter for outputting an error component by subtracting a power level from a theoretical value, and the generation means comprises a second subtracter for subtracting the error component outputted from the first subtracter to the ideal value obtained by an arithmetic means and for outputting a reference level. Thereby, the present invention has the effect that it is not necessary to store the error component and the reference level in a memory table and it is thereby possible to reduce the size of the memory.
According to another aspect of the present invention, there is provided a radio transmitter incorporating an arithmetic means comprising an adder for adding an error component at a reference time to a theoretical value and for outputting an ideal value. Thereby, the present invention has the effect that it is not necessary to store the theoretical value in the memory table and it is thereby possible to further reduce the size of the memory.
According to another aspect of the present invention, there is provided a radio transmitter incorporating an arithmetic means comprising a sample hold circuit for storing an error component at a reference time and for outputting the error component to the adder when receiving a timing signal. Thereby, the present invention has the effect that it is possible to reduce the amount of an arithmetic operation performed by software as small as possible because hardware can perform arithmetic operations for all of the values other than the theoretical value.
According to another aspect of the present invention, there is provided a radio transmission method in which an error component is detected by comparing a power level with a theoretical value, and an ideal value is calculated by adding the error component at a reference time to the theoretical value, and the ideal value is compared with the error component in order to generate a reference level. Thereby, the present invention has the effect that it is possible to preciously suppress the spread of the band of the power spectrum without adjusting the reference power value after manufacturing.
According to another aspect of the present invention, there is provided a radio transmission method in which an error component is detected by comparing a power level with a theoretical value, and a gain of a first amplifier means is controlled based on the detected error component. Thereby, the present invention has the effect that it is possible to accurately suppress the spread of the band of the power spectrum without adjusting the reference power value after manufacturing.
According to another aspect of the present invention, there is provided a radio transmission method in which a theoretical value showing a burst function is calculated by using a window function. Thereby, the present invention has the effect that it is possible to easily obtain the theoretical value showing the burst waveform.
According to another aspect of the present invention, there is provided a radio transmission method in which an envelope curve value is calculated based on a base-band signal, an error component is calculated by comparing the envelope curve value at a reference time with a specified power value, and the theoretical value is then calculated by adding the error component to the envelope curve value per time. Thereby, the present invention has the effect that it is not necessary to calculate the theoretical value by using the window function and it is possible to apply the present invention to the compensation of the distortion in the transmitter chain in the device corresponding to the system based on the linear modulation method.